The Role of Aldehyde Dehydrogenase 2 in Hematopoiesis is Stress-Severity Dependent

Aldehyde dehydrogenase 2 (ALDH2) is a key mitochondrial enzyme that detoxifies reactive aldehydes including formaldehyde, thereby mitigating their genotoxic effects. While ALDH2 deficiency exacerbates bone marrow (BM) failure in Fanconi anemia models, its role under exogenous genotoxic stress is less clear. In this study, we used Aldh2^-/- mice to investigate how ALDH2 deficiency impacts hematopoiesis following treatment with busulfan (BSF), sublethal total body irradiation (TBI), or a combined (BSF+TBI) regimen. Under BSF or TBI monotherapy, Aldh2^-/- mice exhibited moderate increases in DNA damage, measured by γH2AX expression in hematopoietic stem and progenitor cells (HSPCs), with a mild decline in BM cell engraftment, compared to Aldh2^+/+ controls. However, BSF+TBI treatment triggered more severe HSPC DNA damage confirmed by concordant γH2AX and 53BP1 elevation, and a sharper decline in mature hematopoietic cells. Notably, this dual stress significantly upregulated DNA repair and metabolic adaptation genes, including Ccno, Pold4, Taf1c, Npr2, and Aldh18a1. These results suggest that BSF+TBI treatment drives advanced DNA damage and compensatory gene expression shifts in the absence of ALDH2. We conclude that the impact of ALDH2 deficiency on hematopoiesis is dependent on the severity of exogenous stress. TEASER ABSTRACT: The ALDH2 rs671 loss-of-function polymorphism is carried by 30-40% of East Asian individuals, yet its hematopoietic consequences under clinical genotoxic stress remain poorly understood. Using Aldh2^-/- mice, we demonstrate that ALDH2 deficiency increases DNA damage in hematopoietic stem and progenitor cells (HSPCs) following busulfan (BSF) or total body irradiation (TBI) monotherapy, without altering mature hematopoietic cell populations or long-term repopulating capacity. However, combined BSF+TBI treatment unmasks a clear, stress-severity-dependent phenotype: Aldh2^-/- mice exhibit significantly greater HSPC apoptosis and DNA damage confirmed by concordant γH2AX and 53BP1 elevation, and more severe peripheral blood cytopenias. Transcriptomic analysis reveals compensatory upregulation of DNA repair pathways and Aldh18a1, suggesting a metabolic adaptation to mitigate genotoxic burden. These findings establish ALDH2 deficiency as a latent hematopoietic risk factor with direct implications for personalizing conditioning regimens in ALDH2 rs671 carriers undergoing hematopoietic stem cell transplantation.